Process for ink jet printing

ABSTRACT

An ink-jet printing process containing the steps (a) and (b) in any order or simultaneously: (a) applying an ink by means of an ink printer to a localised region of substrate to form an image on the substrate; and (b) applying a fixing composition containing a liquid medium and a polymeric biguanide containing a repeat unit of Formula (1) or a salt thereof by means of an ink jet printer to localised region of the substrate: wherein: X and Y are the same or different and represent divalent organic linking groups; and characterised in that the localised regions referred to in steps (a) and (b) are substantially coextensive.

The present invention relates to an ink jet printing process, to fixingcompositions, to sets of liquids and to ink jet printer cartridges.

Ink-jet printing (IJP) is a non-impact printing technique in whichdroplets of ink are ejected through a fine nozzle onto a substratewithout bringing the nozzle into contact with the substrate. The imagesprepared by IJP desirably meet many demanding requirements. For example,they should be sharp and non-feathered and should also exhibit highwater-fastness, light-fastness, humidity-fastness and optical density.Ideally the images should not blur or run excessively when a highlighterpen is passed over them. Compositions used in IJP should have goodjettability (i.e. low tendency to block the fine nozzles used in ink jetprinters).

Increasingly nowadays highlighter pens are used to draw attention toparticular parts of documents e.g. important sentences. The pen, usuallycontaining a brightly coloured or fluorescent ink, is drawn by thereader over parts of the document they wish to highlight. A problem withmany documents prepared by ink jet printing is that the highlighter cansmear the text, making the important part of the document unsightly oreven unreadable. Thus there is a need to reduce the extent to whichhighlighters cause printed text to smear while at the same time ensuringthe print is of good quality and has high fastness to other sources ofsmear such as sweat.

European Patent 0291214 describes an information device for securityapplications wherein an invisible fixing agent (e.g. a polymericbiguanide) was applied in a localised manner to a substrate and thefixing agent was obscured by over- or under-printing a large area ofsubstrate with an ink. The obscured fixing agent enabled the substrateto carry concealed information which only becomes detectable on e.g.washing of the substrate to selectively remove dye from areas where thefixing agent, was missing. A number of agents could be used to providethe concealed information, including polyhexamethylene biguanide(“PHMB”) having a repeat unit of the formula—(CH₂)₆—HNC(═NH)NH—C(═NH)NH—.

The use of compositions comprising a binder and certain polymericbiguanides in inkjet printing processes was described in InternationalPatent application WO00/37258. The compositions comprising binder andbiguanides were applied to the entire substrate (i.e. not in a localisedmanner) by various coating, spraying or ink jet printing methods.

The costs of replacement cartridges for ink jet printers can also besignificant for small businesses and home users. Ideally ink jetprinters should not waste liquids contained in printer cartridgesbecause this burdens users with high consumables costs.

We have now devised a more efficient process for printing images thanthat described in International Patent Application WO 00/037258.Furthermore, we have surprisingly found that the binder used in thecompositions described in International

Patent Application WO00/037258 is not necessary. Use of biguanide freefrom binder surprisingly displays a number of superior properties tothose compositions described in International Patent ApplicationWO00/37258. In particular the resultant images have good generalwet-fastness and improved resistance to smearing when highlighted usinga highlighter pen.

Thus, according to a first aspect of the present invention there isprovided an ink-jet printing process comprising the steps (a) and (b) inany order or simultaneously:

-   (a) applying an ink by means of an ink jet printer to a localised    region of a substrate to form an image on the substrate; and-   (b) applying a fixing composition comprising a liquid medium and a    polymeric biguanide comprising a repeat unit of Formula (1) or a    salt thereof by means of an ink jet printer to a localised region of    the substrate:

wherein:

X and Y are the same or different and represent divalent organic linkinggroups; and characterised in that the localised regions referred to insteps (a) and (b) are substantially coextensive.

The ink used in step (a) of the process preferably comprises a liquidmedium and a colorant.

Preferred liquid media used in step (a) and/or step (b) include water, amixture of water and an organic solvent and an organic solvent free fromwater.

When the liquid medium used in step (a) and/or step (b) comprises amixture of water and an organic solvent, the weight ratio of water toorganic solvent is preferably from 99:1 to 1:99, more preferably from99:1 to 50:50 and especially from 95:5 to 80:20.

The organic solvent present in the mixture of water and organic solventis preferably a water-soluble organic solvent or a mixture of suchsolvents. Preferred water-soluble organic solvents includeC₁₋₆-alkanols, preferably methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol andcyclohexanol; linear amides, preferably dimethylformamide ordimethylacetamide; ketones and ketone-alcohols, preferably acetone,methyl ether ketone, cyclohexanone and diacetone alcohol; water-solubleethers, preferably tetrahydrofuran and dioxane; diols, preferably diolshaving from 2 to 12 carbon atoms, for example pentane-1,5-diol, ethyleneglycol, propylene glycol, butylene glycol, pentylene glycol, hexyleneglycol and thiodiglycol and oligo- and poly-alkyleneglycols, preferablydiethylene glycol, triethylene glycol, polyethylene glycol andpolypropylene glycol; triols, preferably glycerol and 1,2,6-hexanetriol;mono-C₁₋₄-alkyl ethers of diols, preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially 2-methoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol,2-[2-(2-methoxyethoxy)ethoxy]ethanol,2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether;cyclic amides, preferably 2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, caprolactam and 1,3-dimethylimidazolidone; cyclicesters, preferably caprolactone; sulphoxides, preferably dimethylsulphoxide and sulpholane. Preferably the liquid medium comprises waterand 2 or more, especially from 2 to 8, water-soluble organic solvents.

Especially preferred water-soluble organic solvents are cyclic amides,especially 2-pyrrolidone, N-methyl-pyrrolidone and N-ethyl-pyrrolidone;diols, especially 1,5-pentane diol, ethyleneglycol, thiodiglycol,diethyleneglycol and triethyleneglycol; and mono- C₁₋₄-alkyl andC₁₋₄-alkyl ethers of diols, more preferably mono- C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially2-methoxy-2-ethoxy-2-ethoxyethanol.

Examples of further suitable ink media comprising a mixture of water andone or more organic solvents are described in U.S. Pat. Nos. 4,963,189,4,703,113 and 4,626,284.

When the liquid medium used in step (a) and/or step (b) comprises anorganic solvent free from water, (i.e. less than 1% water by weight) thesolvent preferably has a boiling point of from 30° to 200° C., morepreferably of from 40° to 150° C., especially from 50 to 125° C. Theorganic solvent may be water-immiscible, water-soluble or a mixture ofsuch solvents. Preferred water-soluble organic solvents are any of thehereinbefore described water-soluble organic solvents and mixturesthereof. Preferred water-immiscible solvents include, for example,aliphatic hydrocarbons; esters, preferably ethyl acetate; chlorinatedhydrocarbons, preferably CH₂Cl₂; and ethers, preferably diethyl ether;and mixtures thereof.

When the liquid medium used in step (a) and/or step (b) comprises awater-immiscible organic solvent, preferably a polar solvent is includedbecause this enhances solubility of the dye in the liquid medium.Examples of polar solvents include C₁₋₄-alcohols. In view of theforegoing preferences it is especially preferred that where the liquidmedium is an organic solvent free from water it comprises a ketone(especially methyl ethyl ketone) &/or an alcohol (especially aC₁₋₄-alkanol, more especially ethanol or propanol).

The organic solvent free from water may be a single organic solvent or amixture of two or more organic solvents. It is preferred that when themedium is an organic solvent free from water it is a mixture of 2 to 5different organic solvents. This allows a medium to be selected whichgives good control over the drying characteristics and storage stabilityof the ink.

Liquid media comprising an organic solvent free from water areparticularly useful where fast drying times are required andparticularly when printing onto hydrophobic and non-absorbentsubstrates, for example plastics, metal and glass.

Any colorant suitable for ink-jet printing may be used in the ink.Preferred colorants are pigments which may be organic (including carbonblack) or inorganic, disperse dyes and water-soluble dyes.

Preferred pigments are from the azo, disazo, condensed azo, thioindigo,indanthrone, isoindanthrone, anthanthrone, anthraquinone,isodibenzanthrone, triphendioxazine, quinacridone and phthalocyanineseries of pigments.

Preferred dyes are azo (preferably monoazo, disazo or trisazo),xanthene, phthalocyanine, triphenodioxazine or triarylmethane dyes. Itis especially preferred that the dye(s) are of the azo dyes.

More preferably the colourant comprises a water-soluble azo dye.

The colorant preferably has one or more groups for imparting orassisting water-solubility/dispersibility. Examples of such groupsinclude —COOH, —SO₃H, —PO₃H₂, morpholinyl and piperazinyl and saltsthereof.

When the colorant is a pigment the ink preferably also contains adispersant to give a stable dispersion of the pigment in the ink.Preferably the particle size of the pigment used in the ink is less than1 μm.

The ink may contain a single colorant or a mixture of two or morecolorants.

The colorant is preferably present in the ink at a concentration of 0.5to 20 parts, more preferably from 1 to 15 parts and especially from 1 to5 parts by weight based upon 100 parts total weight of the ink.

The ink may also contain additional components conventionally used inink-jet printing inks, for example viscosity and surface tensionmodifiers, corrosion inhibitors, additives to prevent paper curl,biocides, kogation reducing additives, dispersants and surfactants whichmay be ionic or non-ionic.

In a preferred embodiment of the present invention the colorant has anoverall negative charge when incorporated into the liquid medium.

Examples of particularly favoured colourants are described in EuropeanPatent 356 080, European Patent 468 647, European Patent 679 173,European Patent 559 309. European Patent 0 628 088.

In view of the forgoing preferences particularly preferred inkcomprises:

-   (a) from 0.5 to 20 parts of a pigment or a water-soluble dye;-   (b) from 50 to 98 parts water; and-   (c) from 2 to 50 parts of water-soluble organic solvent(s);    wherein all parts are by weight and the sum of the parts    (a)+(b)+(c)=100.

Preferably the ink and the fixing composition contain less than 500 ppm,more preferably less than 250 ppm, especially less than 100 pm, moreespecially less than 10 ppm in total of divalent and trivalent metalions. The content of halide ions in the ink is preferably below 500 ppm.‘ppm’ means parts per million by weight relative to the total weight ofink.

Preferably the ink and the fixing composition have been filtered througha filter having a mean pore size below 10 μm, more preferably below 3μm, especially below 2 μm, more especially below 1 μm. This filtrationremoves particulate matter that could otherwise block the fine nozzlesused in many ink-jet printers.

The image can be any desired image, for example text, logos, icons ordigital photographs to mention just a few.

The reasons for the localised regions referred to in steps (a) and (b)being substantially coextensive are because if the ink is applied to asignificantly larger area than the fixer then some of the print will notbenefit from improved fixation, leading to smearing and lowerwet-fastness. On the other hand, if the fixer is applied to asignificantly larger area than the ink (e.g. to the entire substrate asdescribed in International Patent Application WO 00/37258) this iswasteful because the fixer is not needed in some of the areas to whichit has been applied and it can lead to unwanted fixation of dirt from ausers hand and spilled beverages such as tea and coffee, resulting inexcessive staining of printed substrates.

Preferably the localised regions referred to in steps (a) and (b) arecoextensive to the extent of at least 80%, more preferably at least 90%,especially 95 to 100% of the total area printed with the ink and fixingcomposition.

The substrate is preferably paper, plastic, a textile, metal or glass,more preferably paper or a plastic film (especially a transparent film,for example an overhead projector slide). It is especially preferredthat the substrate is paper, a textile or a transparent film.

Preferred papers are plain or treated papers which may have an acid,alkaline or neutral character. Examples of commercially availabletreated papers include HP Premium Coated Paper (available from HewlettPackard Inc), HP Photopaper (available from Hewlett Packard Inc), StylusPro 720 dpi Coated Paper, Epson Photo Quality Glossy Film (availablefrom Seiko Epson Corp.), Epson Photo Quality Glossy Paper (availablefrom Seiko Epson Corp.), Canon HR 101 High Resolution Paper (availablefrom Canon), Canon GP 201 Glossy Paper (available from Canon), and CanonHG 101 High Gloss Film (available from Canon).

Preferred plastic films are transparent polymeric films, especiallythose suitable for use as overhead projector slides, for examplepolyesters (especially polyethylene terephthalate), polycarbonates,polyimides, polystyrenes, polyether sulphones, cellulose diacetate andcellulose triacetate films.

Preferred textile materials are natural, synthetic and semi-syntheticmaterials. Examples of preferred natural textile materials include wool,silk, hair and cellulosic materials, particularly cotton, jute, hemp,flax and linen. Examples of preferred synthetic and semi-syntheticmaterials include polyamides, polyesters, polyacrylonitriles andpolyurethanes.

In step (b) in the repeat unit of Formula (1) X and Y are eachindependently optionally interrupted alkylene, more preferablyoptionally interrupted C₂₋₁₂-alkylene and especially C₄₋₆-alkylene;arylene, more preferably C₆₋₁₀-arylene, especially phenylene; andaralkylene, more preferably C₇₋₁₁-aralkylene, especially benzylene orxylylene.

When X and Y are interrupted alkylene, they are preferably interruptedby —O—, —S—, —NH—, —C(═O)— or phenylene.

Examples of preferred alkylene groups represented by X and Y include—(CH₂)₆, —(CH₂)₈—, —CH₂CH(—)(CH₂)₄CH₃, 1,4-2,3- and 1,3-butylene,2,5-hexylen, 2,7-heptylene and 3-methyl-1,6-hexylene.

Examples of preferred interrupted alkylene groups represented by X and Yinclude —CH₂C₆H₄CH₂—, —CH₂OC₆H₄OCH₂—, —CH₂OC₆H₁₀OCH₂—, —(CH₂)₃O(CH₂)₃—and —(CH₂)₂S(CH₂)₂—.

It is especially preferred that X and Y are independently eachC₄₋₆-alkylene. It is more especially preferred that X and Y are bothhexylene.

The nature of the terminating groups on the polymeric biguanide is notbelieved to be critical. However, preferred terminating groups includeacyl, more preferably CH₃CO; H; optionally substituted alkyl, morepreferably optionally substituted C₁₋₁₀alkyl; acyloxy, preferably—OC(O)(C₁₋₄-alkyl); halo more preferably F or Cl; cyano; optionallysubstituted amino; a group of the formula:

and optionally substituted phenyl. Preferred optional substituents onthe terminating groups include C₁₋₄alkyl, halo (especially Cl), nitroand C₁₋₄-alkoxy (especially methoxy). The terminating group at each endof the polymer may be the same or different.

The polymeric biguanide is typically in the form of a mixture of polymerchains, many or all of which are of different lengths. Preferably, thenumber of individual biguanide units in a polymer chain:

taken together, is from 3 to about 80.

In view of the foregoing preferences the polymeric biguanide preferablycomprises one or more poly(hexamethylene biguanide) polymer chains inwhich the individual polymer chains, excluding the terminating groups,are of Formula (2) and salts thereof:

wherein:

n is from 2 to 40.

n is preferably from 2 to 30, more preferably from 4 to 15.

When the polymeric biguanide is a mixture of poly(hexamethylenebiguanide) polymer chains of the Formula (8) it is especially preferredthat the average value of n in the mixture is 12.

Preferably, the number average molecular weight of the polymericbiguanide is from 1100 to 3300.

Preferably the polymeric biguanide is in the form of a salt. Preferredsalts are those with organic or inorganic acids, especiallywater-soluble salts, for example the hydrochloride, gluconate or acetatesalt.

The polymeric biguanides may be prepared by the reaction of abisdicyandiamide of the formula:

with a diamine of the formula H₂N—Y—NH₂; or by reaction between adiamine salt of dicyanimide having the formula:

with a diamine of the formula H₂N—Y—NH₂ wherein X and Y are ashereinbefore defined. These methods of preparation are described in moredetail in GB 702,268 and GB 1,152,243 and any of the polymericbiguanides described therein may be used in the present invention.

The polymeric biguanide is preferably colourless, or substantiallycolourless.

Preferably the ink jet printer used in step (b) is the same ink-jetprinter as that used in step (a).

Preferably the fixing composition and ink are applied in “one pass”,that is the ink and fixing composition are applied during one pass ofthe printing head(s) over the substrate.

The fixing composition is preferably applied to the substrate just priorto, or simultaneously with, application of the ink to the substrate.More preferably the fixing composition is applied to the substrate lessthan 500 milliseconds (ms) prior to the ink. It is especially preferredthat the fixing composition is applied to the substrate less than 100 msprior to the ink.

The ink-jet printer preferably applies the ink (and optionally thefixing composition) to the substrate in the form of droplets which areejected through a small orifice onto the substrate. Preferred ink-jetprinters are piezoelectric ink-jet printers and thermal ink-jetprinters. In thermal ink-jet printers, programmed pulses of heat areapplied to the ink in a reservoir by means of a resistor adjacent to theorifice, thereby causing the ink to be ejected from the orifice in theform of small droplets directed towards the substrate during relativemovement between the substrate and the orifice. In piezoelectric ink-jetprinters the oscillation of a small crystal causes ejection of the inkfrom the orifice. Alternately the ink can be ejected by anelectromechanical actuator connected to a moveable paddle or plunger,for example as described in International Patent Application 00/48938and International Patent Application 00/55089.

Preferably the inkjet printer used to apply the ink and fixingcomposition has a nozzle or a series of nozzles in the printer that arededicated to the application of the fixing composition. Thus the ink-jetprinter may be of the ‘five pen’ type in which yellow, magenta, cyan andblack are applied by four pens and the fixing composition is applied bya fifth pen. A suitable ink-jet printer and a method for its control isdescribed in European Patent 657 849.

The fixing composition is applied to the substrate in substantially thesame localised region as the ink. Thus, the ink-jet printer applies thefixing composition only in that region of the substrate where the inkhas formed an image.

Preferably a drop of ink applied in step (a) either before, after orsimultaneously with the fixing composition applied in step (b) lieswithin the boundaries of the spread drop of the fixing composition.

By limiting the distribution of the fixing agent to the immediate areaof the image the possibility of unwanted stains (e.g. tea or coffee)being bound to the recording sheet by the fixing agent is minimised.Cost savings are also achieved since the amount of fixing agent requiredis reduced.

Preferably the process is free from steps in which the dye is removedfrom the substrate after printing e.g. to form a detectable image.

Application of the fixing agent by means of a ‘fifth’ pen also has theadvantage that printing and fixing can be achieved in one operation andallows the user to easily adjust the level of fixing agent used withdifferent substrates and inks so that optimum performance is achieved.

Preferably the fixing composition in step (b) is free from binders.Binders that are preferably absent from the composition are illustratedby polymeric binders, for example water-soluble or water-dissipatablepolymeric binder and hydrophobic binders. Preferred water-solublebinders include starches, preferably hydroxy alkyl starches, for examplehydroxyethylstarch; celluloses, for example celluslose, methylcellulose,hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethyl methylcellulose, carboxymethlycellulose (and salts thereof) and celluloseacetate butyrate; gelatin; gums, for example guar, xanthan gum and gumarabic; polyvinylalcohol; polyvinylphosphate; polyvinylpyrrolidone;polyvinylpyrrolidine; polyethylene glycol; hydrolysed polyvinylacetate;polyethylene imine; polyacrylamides, for example polyacrylamide andpoly(N,N-dimethyl acrylamide) and polyacrylamido-2-methyl propanesulphonic acid); acrylamide-acrylic acid copolymers; polyvinylpyridine;polyvinylphosphate; vinylpyrrolidone-vinyl acetate copolymers; vinylpyrrolidone-styrene copolymers; polyvinylamine;poly(vinylpyrrolidonedialkylaminoalkyl alkylacrylates), for example polyvinylpyrrolidone-diethylaminomethylmethacrylate; acid-functional acrylicpolymers and copolymers, for example poly(meth)acrylic acid andcopolymers of (meth)acrylic acid and other (meth)acrylate monomers;amine-functional acrylic polymers and copolymers, for examplepolydimethylaminoethylmethacrylate; acid or amine functional urethanepolymers, preferably those containing dimethylolpropanoic acid and/orpendant or terminal polyethylene glycols; ionic polymers, especiallycationic polymers, for example poly (N,N-dimethyl-3,5-dimethylenepiperidinium chloride); polyesters, preferably those which carrywater-solubilising groups, especially sulphonic acid groups, for examplepolyesters obtainable by polymerising a polyol withsodiosulphoisophthalic acid.

Binders have a high boiling point (e.g. above 200° C.) allowing them toremain on the substrate after the fixing composition has dried. Thus inanother preferred embodiment the fixing composition in step (b) is freefrom materials having a boiling point above 200° C. at atmosphericpressure, other than the biguanide.

It is to be understood that in all embodiments of the present inventionthe terms “ink”, “colorant” and “polymeric biguanide” extend to two ormore of these materials respectively as well as one of them.

A preferred fixing composition suitable for use in step (b) comprises:

-   (a) from 0.1 to 10 parts of a polymeric biguanide;-   (b) from 10 to 60 parts of a water-soluble organic solvent; and-   (c) from 35 to 85 parts water,    wherein all parts are by weight and the total number of parts    (a)+(b)+(c)=100.

Preferred water-soluble organic solvents used in the fixing compositionare as described above in relation to liquid media for inks.

When the fixing composition is applied to the substrate by means of anink-jet printer the composition preferably has a viscosity of less than20 cP at 25° C.

Preferably the fixing composition is transparent or colourless when dry.

The prints obtained using the process exhibit low colour bleed, highprint quality and, in many cases, higher light-fastness compared toprints prepared without the polymeric biguanide. Furthermore, theapplication of the fixing agent free from binder does not markedlyaffect the shade or hue of the ink and does not result in thediscoloration of the printed substrate. The absence of binder results isa cheaper fixing composition with improved highlight smear andwater-fastness properties.

According to a second aspect of the present invention there is provideda substrate printed with an image by means of a process according to thefirst aspect of the invention. The preferred substrates are ashereinbefore defined in relation to the first aspect of the presentinvention.

According to a third aspect of the present invention there is provided afixing composition comprising an aqueous medium and a polymericbiguanide as described in the first aspect of the invention,characterised in that the composition is free from binder, has beenfiltered through a filter having a mean pore size below 10 μm andcontains less than 500 ppm total of divalent and trivalent metal ions.

Preferably the composition according to the third aspect of theinvention has been filtered through a filter having a mean pore sizebelow 3 μm, more preferably below 2 μm, especially below 1 μm.

It is also preferred that the composition according to the third aspectof the invention contains less than 250 ppm, more preferably less than100 ppm, especially less than 10 ppm total of divalent and trivalentmetal ions.

The preferred polymeric biguanides and water-soluble organic solventsare as hereinbefore defined in the first aspect of the presentinvention.

According to a fourth aspect of the present invention there is provideda set of liquids suitable for use in an ink-jet printer comprising:

-   (a) a first liquid which is an ink comprising a colorant and a    liquid medium; and-   (b) a second liquid which is a fixing composition comprising:    -   (i) 0.01 to 50 parts, more preferably 0.1 to 30 and especially        from 0.1 to 10 parts of a polymeric biguanide as defined in the        first aspect of the invention; and    -   (ii) 50 to 99.8, more preferably 60 to 80 parts of a liquid        medium preferably selected from water, one or more water-soluble        organic solvents and a mixture of water and one or more        water-soluble organic solvents;        wherein all parts are by weight and the total number of parts        (i)+(ii)=100; and characterised in that the second liquid is        free from binders.

The ink in the set of liquids according to the fourth aspect of thepresent invention is preferably as described above in relation to thefirst aspect of the present invention

The preferred polymeric biguanides, colorants and Water-soluble organicsolvents in the ink set according to the fourth aspect of the presentinvention are as hereinbefore defined in the first aspect of the presentinvention.

The set according to the fourth aspect of the present invention ispreferably housed in an ink-jet printer, i.e. the invention alsoprovides an ink-jet printer comprising a printing mechanism and a set ofliquids as defined in the third aspect of the present invention. Each ofthe liquids may be contained in one or more than one cartridge presentin an ink-jet printer.

A fifth aspect of the invention provides an ink-jet printer cartridgecomprising a plurality of chambers and a set of liquids, wherein theliquids are contained in individual chambers of the ink-jet printercartridge and the set of liquids is as defined in the fourth aspect ofthe invention.

The invention also provides an ink-jet printer cartridge comprising aplurality of chambers and a fixing composition, wherein the fixingcomposition is contained in the chamber of the ink-jet printer cartridgeand the fixing composition is as defined in the first and third aspectsof the invention.

The invention is further illustrated by the following examples in whichall parts and percentages are by weight unless specified otherwise.

In these Examples the following abbreviations are used:

-   -   PHMB hydrochloride is poly(hexamethylene biguanide), obtained        from    -   Avecia Limited as Vantocil™ IB (a 18% solution in water);    -   PEI is Polyethyleneimine, obtained from BASF as Lupasol™ FG;    -   Fast Magenta 2 is a dye obtained from Avecia Limited,        Manchester, England.    -   PVOH is polyvinyl alcohol of molecular weight 13000-23000,        87-89% hydrolysed, obtained from Aldrich Chemical Co. (PVOH is a        binder).

EXAMPLE 1

The following ink and fixing compositions were prepared as follows:

Ink Formulation: Fast Magenta 2 3% 2-Pyrrolidinone 9% Thiodiethyleneglycol 9% Cyclohexanol 2% Deionised Water 77% 

The pH of the ink was adjusted to pH 8.0 with 1 M sodium hydroxide.

Fixing Compositions Fixing Comparative Composition 1 Fixer A PHMB 5% PEI5% 2-Pyrrolidinone 9% 9% Thiodiethylene glycol 9% 9% Cyclohexanol 2% 2%Deionised Water 75%  75% 

The pH of each fixing composition was adjusted to pH 4.0 using 1M nitricacid or 1M sodium hydroxide.

The fixing compositions were placed in the cyan compartment of an emptycolour ink cartridge, and the ink was placed into the yellow chamber ofthe same cartridge. The cartridge was loaded into an Olivetti 102 inkjet printer and the fixing composition was printed onto Xerox Acid paperbefore the ink. In Example 1 the print was under-printed with Fixer 1,in Comparative Example A the print was under-printed with Fixer A and inComparative Example B no fixing composition was applied.

Print Evaluation

Wet-Fastness Assessment

The paper printed with the inks in a pattern of parallel bars wasattached to a support at a 45° angle such that the parallel bars were ina horizontal direction. A pipette was then used to dispense 0.5 ml ofdistilled water (pH 6-7) onto the print at a position slightly above thetop of the parallel bars, taking care to ensure the run down of waterover the print was as close as possible to a right angle to the printedbars.

After allowing the print to dry the average reflected optical density ofthe stained area between printed bars 4 to 6 (“OD Stained”) and theaverage reflected optical density of the unprinted, unstained areas(“Background OD”) were measured using an X rite Spectrodensitometer. Theextent to which the water caused the prints to run into the unprintedarea (i.e. the “Run Down”) was calculated by the equation:Run Down=(OD Stained−Background OD)

A low value of Run Down indicates high water-fastness for the print.

Highlighter Smear

Paper was printed as described above for the wet-fastness assessment.Highlighter smear tests were performed 24 hours after printing using aStabilo Boss yellow highlighter “Stabilo highlighter”, and a SanfordMajor Accent yellow highlighter “Sanford highlighter”. The tests wereperformed by drawing the highlighter twice over unprinted areas of thepaper and then twice over a printed bar and the adjacent unprinted area.The average reflected optical density was measured for unprinted areasof the paper where the highlighter pen had been drawn over twice(“Background OD”). Additionally the average reflected optical densitywas measured for areas of the paper adjacent to printed areas where thehighlighter had been drawn over twice (“OD Smeared”). The extent towhich the highlighter pen caused the prints to smear into the unprintedarea of the paper (i.e. the “Highlighter Smear”) was calculated by theequation:Highlighter Smear=(OD Smeared−Background OD).

The results of the Run Down and Highlighter Smear tests are shown in theTable 1 wherein lower values indicate better wet-fastness and lowerHighlighter Smear as the case may be.

TABLE 1 Comparative Comparative Example Example 1 Example A Example BFixing Composition PHMB PEI None Run Down 0.002 0.001 0.08 StabiloHighlighter Smear 0.02 0.04 0.06 Sanford Hightighter Smear 0.03 0.2 0.08

The results show that using PHMB as under-printing fixer results in lessRun Down (i.e. higher water fastness) than when no fixing agent is used.Furthermore, PHMB results in less Highlighter Smear than with either thecomparative Example A (PEI) or B (no fixing agent).

EXAMPLES 2 AND 3

The following fixing compositions were prepared:

TABLE 2 Fixing Fixing Composition Composition Comparative Comparative 23 Fixer C Fixer D PHMB 5% 2.5%   5% 2.5%   PVOH (binder) 2.5%   2.5%  2-Pyrrolidinone 9% 9% 9% 9% Thiodiethylene 9% 9% 9% 9% glycolCyclohexanol 2% 2% 2% 2% Deionised 75%  77.5%%  72.5%   75%  Water

The pH of each fixing composition was adjusted to pH 4.0 using 1M nitricacid or 1M sodium hydroxide.

The fixing compositions were placed in the cyan compartment of an emptycolour ink cartridge, and the ink was placed into the yellow chamber ofthe cartridge. The cartridges were loaded into an Olivetti 192 printerand the fixing composition was printed onto Weyerhauser First Choicepaper before the ink. In Examples 2 and 3 and comparative Examples C andD the print was under-printed with Fixer 2 and 3 and comparative FixersC and D respectively. In comparative Example E no fixer was used.

Wet-Fastness and Highlighter Smear

The Run Down and Highlighter Smear evaluation tests were performed in ananalogous manner to that described in Example 1 and the results areshown in Table 3 below. Print quality was examined visually and given ascore of 0 to 5 with 5 being perfect quality and 0 being poor quality.

TABLE 3 Comparative Comparative Comparative Example Example 2 Example 3Example C Example D Example E Fixer 5% PHMB 2.5% PHMB 5% PHMB 2.5% PHMBNone 5% PVOH   5% PVOH Run Down 0.01 0.04 0.207 0.198 0.2 Stabilo 0.010.02 0.06 0.1 0.06 Highlighter Smear Sanford 0.04 0.1 0.1 0.1 0.08Highlighter Smear Print 5 5 2 3 5 Quality (0-5)

The results described in Table 3 show that the use of a PHMB in fixingcompositions (Examples 2 and 3) reduces Run Down (i.e. improveswet-fastness) and reduces Highlighter Smear compared to when no PHMB isincluded, particularly in binderless fixing compositions. Furthermore,omission of the binder results in improved print quality compared towhen the binder is present.

1. An ink-jet printing process comprising the steps (a) and (b) in anyorder or simultaneously: (a) applying an ink by means of an ink jetprinter to a localised region of a substrate to form an image on thesubstrate; and (b) applying a fixing composition comprising a liquidmedium and a polymeric biguanide comprising a repeat unit of Formula (1)or a salt thereof by means of an ink jet printer to a localised regionof the substrate:

wherein: X and Y are the same or different and represent divalentorganic linking groups; and characterised in that the localised regionsreferred to in steps (a) and (b) are substantially coextensive andwherein the fixing composition in step (b) is free from binders.
 2. Aprocess according to claim 1 wherein X and Y are independently eachC₄₋₈-alkylene.
 3. A process according to claim 1 wherein X and Y areboth hexylene.
 4. A process according to claim 1 wherein the polymericbiguanide comprises one or more poly(hexamethylene biguanide) polymerchains in which the individual polymer chains, excluding the terminatinggroups, are of Formula (2) and salts thereof:

wherein: n is from 2 to
 40. 5. A process according to claim 1 which isfree from steps in which the dye is removed from the substrate afterprinting.
 6. A process according to claim 1 wherein the ink-jet printeris of the ‘five pen’ type in which yellow, magenta, cyan and black areapplied by four pens and the fixing composition is applied by a fifthpen.
 7. A process according to claim 1 wherein in a drop of ink appliedin step (a) either before, after or simultaneously with the fixingcomposition applied in step (b) lies within the boundaries of the spreaddrop of the fixing composition.
 8. A process according to claim 1wherein the fixing composition in step (b) comprises: (a) from 0.1 to 10parts of a polymeric biguanide; (b) from 10 to 60 parts of awater-soluble organic solvent; and (c) from 35 to 85 parts water;wherein all parts are by weight and the total number of parts(a)+(b)+(c)=100.
 9. A process according to claim 1 wherein the fixingcomposition in step (b) is free from materials having a boiling pointabove 200° C. at atmospheric pressure other than the biguanide.
 10. Asubstrate printed with an image by means of a process according toclaim
 1. 11. A fixing composition comprising an aqueous medium and apolymeric biguanide as described in claim 1, characterised in that thecomposition is free from binder, has been filtered through a filterhaving a mean pore size below 10 μm and contains less than 500 ppm totalof divalent and trivalent metal ions.
 12. A set of liquids suitable foruse in an ink-jet printer comprising: (a) a first liquid which is an inkcomprising a colorant and a liquid medium; and (b) a second liquid whichis a fixing composition comprising: (i) 0.01 to 50 parts of a polymericbiguanide comprising a repeat limit of Formula (1) or a salt thereof

wherein:  X and Y are the same or different and represent divalentorganic linking groups; and (ii) 50 to 99.8 parts of a liquid; whereinall parts are by weight and the total number of parts (i)+(ii)=100; andcharacterised in that the second liquid is free from binders.
 13. Anink-jet printer cartridge comprising a plurality of chambers and a setof liquids, wherein the liquids are contained in individual chambers ofthe ink-jet printer cartridge and the set of liquids is according toclaim
 12. 14. An ink-jet printer cartridge comprising a plurality ofchambers and a fixing composition, wherein the fixing composition iscontained in the chamber of the ink-jet printer cartridge and the fixingcomposition comprises a liquid medium and a polymeric biguanidecomprising a repeat unit of Formula (1) or a salt thereof;

wherein: X and Y are the same or different and represent divalentorganic linking groups; and the fixing composition is free from binders.15. An ink-jet printing process according to claim 1 wherein the ink isnot applied to a significantly larger area than the fixing compositionand the fixing composition is not applied to a significantly larger areathan the ink.
 16. An ink-jet printing process according to claim 1wherein the localised regions referred to in steps (a) and (b) arecoextensive to the extent of at least 80% of the total area printed withthe ink and fixing composition.
 17. An ink-jet printing processaccording to claim 1 which is such that the fixing composition isapplied only to the region where the ink forms an image.